Chelmsford has some flood risk, concentrated in a small part of the city. Only a few postcodes are in the river flood zones. Rainwater raises that to more than one in ten on at least one measure. The climate-adjusted map is bigger again. Most of the city is dry, and a minority of it needs a careful look.
On the Environment Agency's river-and-sea mapping, 4% of the city's postcodes are in Flood Zone 3, the highest-probability band, and a further 3% are in Flood Zone 2, the medium-probability fringe beyond it. The two bands don't overlap, which is why the outer one can be the smaller. The town took shape after the Bishop of London had a bridge built over the River Can in 1100, and it has stayed close to its rivers ever since.
Rivers aren't the only source. Heavy rain that drains badly causes surface-water flooding, and it can reach streets nowhere near the Can or the Chelmer. The river zones leave this out. The broader postcode measure below includes it, so that is where its effect on Chelmsford shows up.
Looking ahead, the Environment Agency's climate-adjusted flood zone covers 8% of the city's postcodes. This models how far the zone could spread under a changing climate, and it gives no date for when any of it might flood.
Insurers price on the exact address, so two houses a few streets apart can be quoted very differently, and a home in the higher zones may cost noticeably more to cover. Put the exact address into the Environment Agency's long-term flood risk service and get an indicative insurance quote while the purchase is still at an early stage. A vendor who says the house has "never flooded" usually means it hasn't flooded since they bought it.
At postcode level, counting any of several flood measures including surface water, 13% of the city's postcodes are rated high on at least one, 20% medium and 41% low. These shares are separate from the zone figures above, because each postcode counts once under whichever measure gives it the highest rating.
Counting homes gives a different view. The Environment Agency's rivers-and-sea assessment lists 5,201 properties in 202 postcodes that carry some risk. Of those, 126 are at high risk, 90 of them residential, 1,560 are at medium risk, 1,732 at low risk and 118 at very low risk. Postcodes with no risk on that measure are left out entirely, so the total counts only properties with some exposure and is smaller than the city's housing stock.
Within the modelled high-probability flood extent, 5% of the city's postcodes have no defence in the model and 4% have one. That means a defence appears in the Environment Agency's model. It doesn't tell you about its condition, its height or how a particular house will fare. A defence improves the odds and leaves the river where it is.
The nearest coast is about nine kilometres from the city, and only 7% of its postcodes are covered by a shoreline management plan at all. For those, the stated policy is to hold the line for the next 20 years, the next 50 and the next 100. A policy states what the authorities intend, depends on money that hasn't been committed, and says nothing about the defences that exist today. Hold the line is a promise about a coastline most of Chelmsford can't see.
Overall, Chelmsford's flood risk is middling. Most homes are well clear of the water, and the ones that aren't are usually near enough to the Can or the Chelmer for their owners to know it.